JPH0521517A - Flip chip bonding method and substrate used therefor - Google Patents

Abstract

PURPOSE:To easily form a solder bump in a columnar shape in bonding a flip chip to a substrate. CONSTITUTION:A metallic ball 20 is seated in a recessed section 18 formed on a substrate 8, with a soldering material 22 being brought into contact with the ball 20, so that the ball 20 can move to the outside of the section 18 by the surface tension of the material 22 when the material 22 is melted and can get in between an element chip 2 and the substrate 8 when solder bumps 6 harden.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip bonding method for electrically and mechanically connecting an element chip such as a semiconductor circuit element chip and a substrate on which the element chip is mounted, and a substrate used for implementing the method. Regarding

As a method of mounting an element chip in an electronic circuit device, there is known a mounting method such as wire bonding or TAB in which electrical wiring of terminals is performed on the outer periphery of the chip.

However, in recent years, the number of terminals of the element chip has increased along with the high performance and multi-functionalization of the element chip, which cannot be dealt with by the above-mentioned mounting method such as wire bonding. .

Therefore, research and development on flip chip bonding capable of connecting terminals on the entire surface of the element chip have been vigorously carried out at various places, and optimization of the shape of solder bumps and the like has been sought.

[0005]

2. Description of the Related Art Conventionally, as shown in FIG. 4A, a solder bump 6 formed on an electrode 4 of an element chip 2 is contacted with a conductor pattern 10 on a substrate 8 to form the solder bump 6. A flip chip bonding method is known in which the electrodes 4 and the conductor pattern 10 are melted and connected to each other.

According to this method, the shape of the solder bump after joining becomes spherical due to the surface tension at the time of melting. In this case, since the cross-sectional area of the solder bump in the vicinity of the joint is smaller than the cross-sectional area of the central portion, stress concentration is likely to occur in the joint indicated by A and B, and there is a problem that the mechanical strength decreases. In view of such a point, it has been proposed that the solder bumps 6 have a columnar shape as shown in FIG.

A comparison of stresses due to differences in the shape of solder bumps has been studied by Ryohei Sato (Journal of the Japan Institute of Metals, Vol. 51, No. 6 (1987), pp.553-560 "I").
C, Optimal connection shape control of LSI fine solder joints ").

FIG. 5 is a graph in which the relationship between the maximum equivalent stress σ and the bump height h _i when the volume of the solder bump is constant is plotted for each amount d proportional to the bump interval. The maximum equivalent stress σ can be significantly reduced by increasing the bump height h _i and forming the solder bump into a columnar shape.

[0009]

Next, a conventional method for forming the solder bump into a columnar shape and its problems will be described.

The first conventional method shown in FIG. 6 is as shown in FIG.
As shown in FIG. 6A, when the solder bump 6 is melted, the element chip 2 is pulled upward by the suction nozzle 12 so as to resist the surface tension thereof, and as shown in FIG. 6B, the melted solder bump 6 is melted. Is cooled in a columnar shape.

According to this method, in order to make the heights of a plurality of solder bumps uniform, it is necessary to support the element chip 2 and the substrate 8 accurately in parallel, which complicates the structure of the device. There is a problem.

In the second conventional method shown in FIG. 7, the solder bumps 6 are stacked in multiple stages via at least one (two in the figure) film 14 made of polyimide or the like, and are equivalently columnar solder bumps. It is a structure. This method is disclosed in the following document. Sasaki et al., "Terminal Connection of Large Chip by Multi-Solder Bump Method", 1986 National Conference of Communication Society, No. 506 This method involves difficulty in the work for stacking the solder bumps in multiple stages and without misalignment.

In the third conventional method shown in FIG. 8, a height control bump 16 made of a solder having a larger volume and a higher melting temperature than the solder bump 6 for electrical connection is arranged in the central portion of the chip, By using the surface tension generated in the height control bumps 16, the element chip 2 is lifted upward to move the solder bumps 6
Is to be columnar.

According to this method, two kinds of soldering materials having different melting temperatures are required and the method becomes complicated, and
There arises a problem that electrical connection cannot be made on the entire surface of the element chip.

As described above, the conventional method is complicated, and realization of a simple flip chip bonding method is desired.
The present invention has been made in view of the above technical problems, and an object thereof is to provide a simple flip chip bonding method in which the shape of a solder bump can be formed into a columnar shape, and a substrate used for carrying out this method. I am trying.

[0016]

The above-mentioned technical problems are as follows.
It is solved by the first or second configuration of the substrate of the present invention or by the first or second flip chip bonding method of the present invention.

The first structure of the substrate of the present invention is to melt the solder bumps in a state where the solder bumps formed on the electrodes of the element chip are in contact with the conductor patterns on the substrate to melt the solder bumps. In the substrate used for carrying out the flip chip bonding method for connecting, a recess for seating a metal ball for regulating the gap between the element chip and the substrate is formed on the surface of the element chip side, A solder material that comes into contact with the metal balls is provided near the recess.

The second structure of the substrate of the present invention is to melt the solder bumps in a state where the solder bumps formed on the electrodes of the element chip are in contact with the conductor patterns on the substrate to melt the electrodes and the conductor patterns. A first and second recesses having different depths for seating metal balls for restricting a gap between the element chip and the substrate, the substrate being used for implementing a flip chip bonding method for connecting A solder material that is formed on the surface of the element chip side and is in contact with the metal balls is provided in the second recess.

The first flip-chip bonding method of the present invention is a method using the first configuration of the substrate of the present invention, in which the metal ball is seated in the recess and the solder bump is provided with the conductor pattern. And a step of melting the solder bumps and the solder material, moving the element chip away from the substrate, and moving the metal balls to the outside of the recess by the surface tension of the melted solder material, Solidifying the solder bumps and the solder material with the metal balls interposed between the element chip and the substrate.

A second flip chip bonding method of the present invention is a method using the second structure of the substrate of the present invention, in which the metal ball is seated in the first recess and the solder bump is attached. Contacting the conductor pattern, melting the solder bump and the solder material, moving the element chip away from the substrate, and the surface tension of the melted solder material causes the metal ball to move to the first hollow. To the second recess, and coagulating the solder bump and the solder material with the metal ball interposed between the element chip and the second recess.

[0021]

According to the first flip chip bonding method of the present invention, the surface tension of the molten solder material causes the metal balls to move out of the recesses, and the solder balls are interposed between the element chip and the substrate. Since the element is solidified, the distance between the element chip and the substrate is regulated by the metal balls, and the solder bump can be shaped like a column.

When a plurality of metal balls having the same diameter are used, the element chip and the substrate are kept parallel to each other when the solder bumps are solidified. The height of the formed solder bumps can be made uniform.

As described above, according to the method of the present invention, the shape of the solder bump can be easily made columnar. According to the second flip chip bonding method of the present invention, the metal ball moved from the first recess is seated in the second recess due to the surface tension of the molten solder material. It is prevented that the solder bumps are dropped again, and the shape of the solder bumps can be surely made cylindrical.

[0024]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a process explanatory diagram showing a first embodiment of the present invention. Reference numeral 2 is an element chip, and 4 is an electrode for electrically connecting the element chip 2 to the outside. A solder bump 6 is fixed to the electrode 4 in advance. The element chip 2 is sucked and sucked by the suction nozzle 12 and conveyed to a predetermined position on the substrate 8.

A conductor pattern 10 is formed on the substrate 8 at a position corresponding to the electrode 4. Also on the substrate 8
For example, a recess 18 having a V-shaped cross section is formed, and a metal ball 20 can be seated in this recess 18.

A conductor pattern 24 is formed in the vicinity of the recess 18, and the solder material 22 is formed on the conductor pattern 24.
Is stuck. The solder material 22 is shaped so as to come into contact with the metal ball 20 seated in the recess 18.

First, as shown in FIG. 1A, a metal ball 20 is previously seated in the recess 18 of the substrate,
The position of the element chip 2 is determined by the suction nozzle 12 so that the electrode 4 of the element chip faces the conductor pattern 10 of the substrate.

Then, the element chip 2 is lowered to bring the solder bumps 6 fixed in advance on the electrodes 4 into contact with the conductor patterns 10 on the substrate. In this case, it is desirable that the diameter of the metal ball 20 is set so that the upper end of the metal ball 20 seated in the recess 18 contacts the lower surface of the element chip 2.

Next, after the solder bumps 6 and the solder material 22 are heated and melted, the suction nozzle 12 raises the element chip 2 upward in the drawing. The displacement amount of the element chip 2 is set to such an extent that the melted solder bump is not separated into the element chip 2 side and the substrate 8 side.

Since the solder material 22 before melting contacts the metal balls 20 seated in the depressions 18, when the element chip 2 is raised, the melted solder material 22
The surface tension generated on the metal ball 20 acts in the direction of moving the metal ball 20 out of the recess 18, and as a result, the metal ball 20 moves to the outside of the recess 18 and moves toward the flat surface of the substrate 8 as shown in FIG. Will be located above.

When the element chip 2 is lifted by the nozzle 12, in order to improve the wettability of the molten solder bump 6 to the conductor pattern 10, the element chip 2 is slightly vibrated in the horizontal direction in the drawing, so-called scrubbing. It is desirable to do.

Then, as shown in FIG. 1C, the suction of the element chip 2 by the suction nozzle 12 is stopped, and cooling is performed with the metal ball 20 interposed between the element chip 2 and the substrate 8. Then, the solder bumps 6 and the solder material 22 are solidified.

At this time, since the distance between the element chip 2 and the substrate 8 is regulated by the metal balls 20, the solidified solder bump 6 has a columnar shape. Generally, since there are many electrodes of the element chip to be connected to the conductor pattern on the substrate by solder bumps, it is desirable to carry out the method of the present invention using a plurality of metal balls. When a plurality of metal balls are used, the parallelism between the element chip and the substrate is maintained when the solder bumps and the solder material are solidified by arranging the plurality of metal balls in a grid pattern, for example, and the height of the columnar solder bumps is increased. Can be constant.

According to this embodiment, complicated temperature control and stress control as in the above-mentioned third conventional method are unnecessary,
It is easy to form the solder bump into a pillar shape. FIG. 2 is an explanatory diagram of the second embodiment of the present invention. In this embodiment, the first and second recesses 2 for seating the metal balls 20 are provided.
6 and 28 are formed on the surface of the substrate 8 on the element chip side so as to be close to each other. The depth d ₁ of the _first depression 26 is set larger than the depth d ₂ of the second depression 28.

Reference numeral 30 is a conductor pattern formed so as to cover the second recess 28, and reference numeral 32 is a solder material provided on the second recess 28. In this embodiment, first, as shown in FIG. 2 (A), the metal ball 20 is seated in the first recess 26, and the solder material 32 is used as the metal ball 2.
Keep in contact with 0.

Then, when the solder bumps and the solder material 32 are melted in the same manner as in the previous embodiment, as shown in FIG.
As shown in (B), the metal ball 20 moves from the first recess 26 to the second recess 28 due to the surface tension of the solder material 32.

According to the present embodiment, the metal ball 20 that has moved onto the second recess 28 is seated in this recess, so that there is no risk that the metal ball 20 will drop into the first recess 26 again.

FIG. 3 is an explanatory view of the third embodiment of the present invention. This embodiment is a modification of the first embodiment, and when the solder bump 6 and the solder material 22 are solidified, the solder bump 6
The metal balls 20 are pressed against the electrodes 34 formed on the element chip 2 by the contracting force of the solder bumps 6
The electrodes 34 of the element chip 2 and the conductor pattern 24 of the substrate 8 are electrically connected not only by the solidified solder material 22 and the metal balls 20 but also by the solidified solder material 22 and the metal balls 20.

According to this embodiment, since the number of wiring channels per unit area can be increased, the space can be effectively used. When carrying out the method of the present invention, it is necessary to previously seat the metal balls in the depressions, but the initial arrangement of the metal balls is to slide a large number of metal balls on the slightly tilted substrate. Can be done automatically.

[0040]

As described above, according to the present invention,
It is possible to provide a simple flip chip bonding method in which the shape of the solder bump can be formed into a pillar shape, and a substrate used for carrying out the method can be provided.

[Brief description of drawings]

FIG. 1 is a process explanatory diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of flip chip bonding.

FIG. 5 is a graph showing a comparison of stresses due to different shapes of solder bumps.

FIG. 6 is an explanatory diagram of a first conventional method.

FIG. 7 is an explanatory diagram of a second conventional method.

FIG. 8 is an explanatory diagram of a third conventional method.

[Explanation of symbols]

2-element chip 4,34 electrodes 6 Solder bump 8 substrates 10, 24, 28 conductor pattern 18 dimples 20 metal balls 22,32 Solder material 26 First depression 28 Second depression

Claims (6)

[Claims] 1. A solder bump (6) formed on an electrode (4) of an element chip (2) is contacted with a conductor pattern (10) on a substrate (8), and the solder bump (6) is attached to the conductor bump (6). Melted above electrode
A substrate (8) used for carrying out a flip-chip bonding method for connecting (4) and the conductor pattern (10), wherein a gap between the element chip (2) and the substrate (8) is regulated. A recess (18) for seating the metal ball (20) is formed on the surface of the element chip (2) side, and a solder material (22) contacting the metal ball (20) is provided in the vicinity of the recess (18). ) Is provided. 2. A solder bump (6) formed on an electrode (4) of an element chip (2) is contacted with a conductor pattern (10) on a substrate (8), and the solder bump (6) is attached to the conductor bump (6). Melted above electrode
A board (8) used for carrying out a flip chip bonding method for connecting (4) and the conductor pattern (10), wherein a gap between the element chip (2) and the board (8) is regulated. For seating metal balls (20) for
And second recesses (26, 28) are formed on the surface of the element chip (2) side, and the second recess (28) is provided with a solder material (32) contacting the metal balls (20). A substrate characterized by being provided. 3. A flip-chip bonding method using the substrate (8) according to claim 1, wherein the metal ball (20) is seated in the recess (18) to form the solder bump (6). The step of contacting with the conductor pattern (10), melting the solder bumps (6) and the solder material (22), moving the element chip (2) away from the substrate (8), and melting the solder material The step of moving the metal ball (20) out of the recess (18) by the surface tension of the metal ball (20),
A flip chip bonding method comprising the step of solidifying the solder bump and the solder material in a state of being interposed between (8). 4. A flip chip bonding method using the substrate (8) according to claim 2, wherein the metal ball (20) is seated in the first recess (26) and the solder bump ( 6) contacting the conductor pattern (10), melting the solder bumps (6) and the solder material (32), separating the element chip (2) from the substrate (8), and melting. The step of moving the metal ball (20) from the first recess (26) to the second recess (28) by the surface tension of the solder material; 2) and a step of solidifying the solder bump and the solder material while being interposed between the second recess (28) and the second recess (28). 5. The element chip (2) and the substrate according to the solidified solder material (22, 32) and the metal ball (20).
(8) is electrically connected to (3).
Or the flip chip bonding method described in 4. 6. The flip chip bonding method according to claim 3, wherein a plurality of the metal balls (20) having the same diameter are used.